U.S. patent application number 15/171051 was filed with the patent office on 2016-09-22 for cover glass for light emitting diode package, sealed structure, and light emitting device.
This patent application is currently assigned to Asahi Glass Company, Limited. The applicant listed for this patent is Asahi Glass Company, Limited. Invention is credited to Yoko MITSUI, Makoto SHIRATORI, Satoshi TAKEDA.
Application Number | 20160276544 15/171051 |
Document ID | / |
Family ID | 53371117 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160276544 |
Kind Code |
A1 |
SHIRATORI; Makoto ; et
al. |
September 22, 2016 |
COVER GLASS FOR LIGHT EMITTING DIODE PACKAGE, SEALED STRUCTURE, AND
LIGHT EMITTING DEVICE
Abstract
To provide a cover glass for light emitting diode package, which
is capable of preventing deterioration in transmittance
characteristics during use for a long period of time, and a light
emitting device. The cover glass for light emitting diode package
has a basic composition comprising, by mass % as calculated as
oxides, from 55 to 80% of SiO.sub.2, from 0.5 to 15% of
Al.sub.2O.sub.3, from 5 to 25% of B.sub.2O.sub.3, from 0 to 7% of
Li.sub.2O, from 0 to 15% of Na.sub.2O, from 0 to 10% of K.sub.2O
(provided Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%), from 0 to
0.1% of SnO.sub.2 and from 0.001 to 0.1% of Fe.sub.2O.sub.3, it
does not substantially contain As.sub.2O.sub.3, Sb.sub.2O.sub.3 and
PbO, and it has an average thermal expansion coefficient of from 45
to 70.times.10.sup.-7/.degree. C. in a temperature range of from 0
to 300.degree. C.
Inventors: |
SHIRATORI; Makoto;
(Haibara-gun, JP) ; MITSUI; Yoko; (Chiyoda-ku,
JP) ; TAKEDA; Satoshi; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asahi Glass Company, Limited |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
Asahi Glass Company,
Limited
Chiyoda-ku
JP
|
Family ID: |
53371117 |
Appl. No.: |
15/171051 |
Filed: |
June 2, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2014/082305 |
Dec 5, 2014 |
|
|
|
15171051 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 8/24 20130101; H01L
33/483 20130101; C03C 3/11 20130101; H01L 33/56 20130101; H01L
2924/16195 20130101; C03C 3/093 20130101; C03C 3/091 20130101; H01L
33/507 20130101; H01L 2933/0033 20130101; H01L 33/32 20130101 |
International
Class: |
H01L 33/48 20060101
H01L033/48; C03C 3/11 20060101 C03C003/11; C03C 3/093 20060101
C03C003/093; C03C 3/091 20060101 C03C003/091 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2013 |
JP |
2013-256170 |
Claims
1. A cover glass for light emitting diode package, characterized in
that it has a basic composition comprising, by mass % as calculated
as oxides, from 55 to 80% of SiO.sub.2, from 0.5 to 15% of
Al.sub.2O.sub.3, from 5 to 25% of B.sub.2O.sub.3, from 0 to 7% of
Li.sub.2O, from 0 to 15% of Na.sub.2O, from 0 to 10% of K.sub.2O
(provided Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%), from 0 to
0.1% of SnO.sub.2 and from 0.001 to 0.1% of Fe.sub.2O.sub.3, it
does not substantially contain As.sub.2O.sub.3, Sb.sub.2O.sub.3 and
PbO, and it has an average thermal expansion coefficient of from 45
to 70.times.10.sup.-7/.degree. C. in a temperature range of from 0
to 300.degree. C.
2. The cover glass for light emitting diode package according to
claim 1, characterized in that it has a basic composition
comprising, by mass % as calculated as oxides, from 55 to 80% of
SiO.sub.2, from 0.5 to 15% of Al.sub.2O.sub.3, from 5 to 25% of
B.sub.2O.sub.3, from 0 to 7% of Li.sub.2O, from 0 to 15% of
Na.sub.2O, from 0 to 10% of K.sub.2O (provided
Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%), from 0 to 0.1% of
SnO.sub.2 and from 0.003 to 0.1% of Fe.sub.2O.sub.3, it does not
substantially contain As.sub.2O.sub.3, Sb.sub.2O.sub.3 and PbO, and
it has an average thermal expansion coefficient of from 45 to
70.times.10.sup.-7/.degree. C. in a temperature range of from 0 to
300.degree. C.
3. The cover glass for light emitting diode package according to
claim 1, characterized in that the transmittance at a wavelength of
365 nm in a thickness of 1 mm is at least 85%.
4. The cover glass for light emitting diode package according to
claim 1, characterized in that the average transmittance at a
wavelength of from 808 to 1,064 nm in a thickness of 1 mm is at
least 85%.
5. The cover glass for light emitting diode package according to
claim 1, characterized in that the refractive index (nd) is at most
1.52.
6. A sealed structure having a cover glass and a light emitting
diode package bonded to each other, characterized in that a light
emitting diode package and the cover glass for light emitting
package as defined in claim 1 are bonded.
7. A sealed structure having a cover glass and a light emitting
diode package bonded to each other, characterized in that the light
emitting diode package is made of a glass ceramic substrate
obtained by firing a glass ceramic composition containing a glass
powder and a ceramic filler, and such a glass ceramic substrate and
the cover glass for light emitting package as defined in claim 1
are bonded.
8. The sealed structure having a cover glass and a light emitting
diode package bonded to each other, according to claim 6,
characterized in that the cover glass is bonded to the light
emitting diode package via a low melting point glass which is
melted by laser irradiation
9. A light emitting device characterized by comprising a cover
glass for light emitting diode package as defined in claim 1, a
light emitting diode package having a light emitting diode mounted
thereon, and a sealing material containing a low melting point
glass which is melted by laser irradiation to bond the cover glass
for light emitting diode package and the light emitting diode
package.
10. The light emitting device according to claim 9, wherein the
sealing material comprises the low melting point glass and an
inorganic filler.
11. The light emitting device according to claim 10, wherein the
inorganic filler is at least one member selected from a
low-expansion filler and an electromagnetic wave absorbing
material.
12. The light emitting device according to claim 9, wherein the
difference in average thermal expansion coefficient in a
temperature range of from 25 to 300.degree. C. between the light
emitting diode package and the cover glass for light emitting diode
package is at most 20.times.10.sup.-7/.degree. C.
13. The light emitting device according to claim 9, wherein the
light emitting diode package is made of a glass ceramic substrate
obtained by firing a glass ceramic composition containing a glass
powder and a ceramic filler, and between the average thermal
expansion coefficient in a temperature range of from 25 to
300.degree. C. of the glass ceramic substrate and the average
thermal expansion coefficient in a temperature range of from 25 to
300.degree. C. of the cover glass for light emitting diode package,
there is a relation of "the average thermal expansion coefficient
of the glass ceramic substrate".gtoreq."the average thermal
expansion coefficient of the cover glass for light emitting diode
package".
Description
TECHNICAL FIELD
[0001] The present invention relates to a light emitting device
using a light emitting diode as a light source, a cover glass for
light emitting diode package to be used for the device, and a
sealed structure having the cover glass.
BACKGROUND ART
[0002] A light emitting device using a light emitting diode as a
light emitting source is one to obtain light emission of a desired
color by letting light be emitted from a light emitting diode chip
and subjecting the emitted light to wavelength conversion by a
phosphor.
[0003] For example, in order to obtain white light by a light
emitting device, blue light is permitted to be generated by a light
emitting diode chip of gallium nitride (GaN) type, and the blue
light is permitted to pass through a wavelength conversion layer
that holds a phosphor of yttrium aluminum.cndot.garnet (YAG) type.
Thus, light from red to green obtained as fluorescence is combined
with blue color passed through the phosphor, whereby it is possible
to obtain emission of white light.
[0004] The above wavelength conversion layer is such that one
obtained by dispersing various phosphors to e.g. a resin component,
is placed on the light emitting diode chip. Therefore, due to the
heat radiation from the light emitting diode chip itself and the
oxygen component in the atmosphere, deterioration of the wavelength
conversion performance by long-term use is worried.
[0005] Whereas, a construction has been proposed wherein a
plate-form protection member is provided which has a light
transmittance with respect to light emitted from a light emitting
diode chip and which is air-tightly secured to a package body in
such a form to close a housing recess on one surface side of a
semiconductor substrate (see Patent Document 1). According to this
construction, it is possible to protect a light emitting diode chip
housed inside, from mechanical destruction factors or environmental
destruction factors from outside, without using a conventional
sealing resin, and thus, it is possible to improve the
reliability.
PRIOR ART DOCUMENT
Patent Document
[0006] Patent Document 1: JP-A-2005-166733
DISCLOSURE OF INVENTION
Technical Problem
[0007] In the light emitting diode package as disclosed in the
above mentioned prior art document, a package body made of a
silicon substrate and a protective member made of a glass substrate
are said to be fixed by anodic bonding or surface activated
bonding. However, if the substrate material of the package body is
different from silicon, it is not possible to sufficiently prevent
lowering of airtightness caused by the difference in thermal
expansion coefficient between the package body and the protective
member.
[0008] The present invention is to solve the above problem and has
an object to provide a cover glass for light emitting diode
package, capable of preventing deterioration of the transmittance
characteristics during use for a long period of time, a sealed
structure having the cover glass and the light emitting diode
package bonded to each other, and a light emitting device.
Solution to Problem
[0009] In order to accomplish the above object, the cover glass for
light emitting diode package according to the present invention is
characterized in that it has a basic composition comprising, by
mass % as calculated as oxides, from 55 to 80% of SiO.sub.2, from
0.5 to 15% of Al.sub.2O.sub.3, from 5 to 25% of B.sub.2O.sub.3,
from 0 to 7% of Li.sub.2O, from 0 to 15% of Na.sub.2O, from 0 to
10% of K.sub.2O (provided Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to
20%), from 0 to 0.1% of SnO.sub.2 and from 0.001 to 0.1% of
Fe.sub.2O.sub.3, it does not substantially contain As.sub.2O.sub.3,
Sb.sub.2O.sub.3 and PbO, and it has an average thermal expansion
coefficient of from 45 to 70.times.10.sup.-71.degree. C. in a
temperature range of from 0 to 300.degree. C.
[0010] Further, the cover glass for light emitting diode package
according to the present invention is characterized in that it has
a basic composition comprising, by mass % as calculated as oxides,
from 55 to 80% of SiO.sub.2, from 0.5 to 15% of Al.sub.2O.sub.3,
from 5 to 25% of B.sub.2O.sub.3, from 0 to 7% of Li.sub.2O, from 0
to 15% of Na.sub.2O, from 0 to 10% of K.sub.2O (provided
Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%), from 0 to 0.1% of
SnO.sub.2 and from 0.003 to 0.1% of Fe.sub.2O.sub.3, it does not
substantially contain As.sub.2O.sub.3, Sb.sub.2O.sub.3 and PbO, and
it has an average thermal expansion coefficient of from 45 to
70.times.10.sup.-7/.degree. C. in a temperature range of from 0 to
300.degree. C.
[0011] Further, the sealed structure having a cover glass and a
light emitting diode package bonded to each other, according to the
present invention, is characterized in that the above cover glass
and a light emitting diode package are bonded.
[0012] Further, the light emitting device according to the present
invention is characterized by comprising the above cover glass for
light emitting diode package, the above light emitting diode
package having a light emitting diode mounted thereon, and a
sealing material containing a low melting point glass which is
melted by laser irradiation to bond the cover glass for light
emitting diode package and the light emitting diode package.
[0013] The expression "to" indicating a numerical range in this
specification, is used in the sense to include the numerical values
described before and after the expression as the minimum value and
the maximum value, and unless otherwise specified, hereinafter in
this specification, "to" is used to have the same meaning.
Advantageous Effects of Invention
[0014] According to the present invention, it is less likely that
hermetic sealing of the light emitting diode package having a light
emitting diode mounted thereon and the cover glass for light
emitting diode package is broken by e.g. a temperature change, and
therefore, it is possible to prevent deterioration of the
transmittance characteristics during use for a long period of
time.
BRIEF DESCRIPTION OF DRAWING
[0015] FIG. 1 is a schematic sectional view of a cover glass for
light emitting diode package and a light-emitting device according
to an embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0016] One embodiment of the cover glass for light emitting diode
package and the light emitting device of the present invention will
be described with reference to the drawing.
[0017] A light emitting device 1 of this embodiment as shown in
FIG. 1, comprises a light emitting diode chip (hereinafter referred
to also as a light emitting diode) 3, a light emitting diode
package 5 (hereinafter referred to also as a package 5) having the
light emitting diode chip 3 mounted thereon, a wavelength
conversion member 2 disposed on the light emitting diode chip 3, a
cover glass 4 for light emitting diode package (hereinafter
referred to as a cover glass 4), that is hermetically sealed to
cover the opening of the package 5, and a sealing material 6 for
bonding the package 5 and the cover glass 4. The light emitting
device 1 of this embodiment is one to be used for e.g. a light
source for various luminaires, or an operation display unit for
electronics.
[0018] The package 5 is provided with a recess, and the light
emitting diode chip 3 is mounted on the bottom surface of the
recess. Further, wiring (not shown) to connect the light emitting
diode chip 3 and an electrode portion (not shown) provided outside
of the package 5, is provided inside the package 5.
[0019] As the package 5, one made of a glass ceramic substrate
obtained by firing a glass ceramic composition containing a glass
powder and a ceramic filler (low-temperature co-fired ceramic
substrate; hereinafter sometimes referred to as LTCC), may be
mentioned as a typical example and is preferably used. Further, a
light reflecting layer such as silver which reflects light from
e.g. the light emitting diode chip may be provided on the inner
surface of the recess of the package 5. In consideration of the
long-term reliability, such a light reflecting layer may be
constructed so that a conductive layer made of silver is covered
with an overcoat glass made of glass.
[0020] As the material for the package 5, as an example other than
the above-mentioned glass ceramic substrate, alumina, silicon
nitride, aluminum nitride, silicon carbide, etc. may be
mentioned.
[0021] LTCC contains a glass powder and a ceramic filler, has a
larger difference between the refractive index of the glass and the
refractive index of the ceramic filler, and can increase the amount
of the ceramic filler dispersed in the LTCC. Thus, the area of the
interface which reflects light becomes large, and further, the
thickness of the glass or the ceramic filler at both sides of the
interface can be made larger than the wavelength of light, whereby
the reflectance is high. Therefore, the package made of LTCC can
efficiently reflect light from the light emitting element, and as a
result, heat generation can be reduced.
[0022] Further, since it is formed from an inorganic oxide such as
glass powder or ceramic filler, LTCC is free from degradation due
to a light source unlike a resin substrate, and it is possible to
maintain the color tone stability over a long period of time.
[0023] Usually, LTCC can be formed in the following manner. That
is, firstly, a raw material powder composed mainly of a glass
powder and a ceramic filler (ceramic powder) is mixed with a resin
such as polyvinyl butyral or an acrylic resin, if necessary, by
adding e.g. a plasticizer such as dibutyl phthalate, dioctyl
phthalate or butyl benzyl phthalate. Then, a solvent such as
toluene, xylene or butanol, is added to prepare a slurry, and this
slurry is molded into a sheet by a doctor blade method or the like
on a film of e.g. polyethylene terephthalate. Finally, the one thus
having molded into a sheet is dried to remove the solvent to obtain
a green sheet. In such a green sheet, as the case requires, a
wiring pattern, a via-hole being a through-conductor, etc. may be
formed by e.g. screen printing using a silver paste, a silver
conductor or the like. In some cases, it is also possible to form
an overcoat glass by e.g. screen printing to protect wirings, etc.
formed of silver.
[0024] The above green sheet is fired and then processed into a
desired shape to obtain a glass ceramic substrate. In this case,
the body to be fired is a single green sheet or a laminate having a
plurality of same green sheets overlaid one on another.
[0025] Further, as LTCC, the green sheet may be provided with
through-holes, and a powder of a silver conductor or copper
conductor having a high heat conductivity is made into a paste and
embedded into the through-holes, followed by firing at the same
time as the powder of the silver conductor or copper conductor,
whereby it is possible to efficiently produce a glass ceramic
substrate with through conductors having excellent heat dissipation
properties.
[0026] The ceramic filler as a component of the glass ceramic
composition may, for example, be alumina, titania or zirconia. It
is possible to increase the strength of the substrate by
incorporating an alumina filler. In order to increase the strength
of the substrate, it is preferred to incorporate an alumina filler
in an amount of at least 30 mass % in the composition.
[0027] The glass powder as a component of the glass ceramic
composition is usually prepared by pulverizing glass obtained by a
melting method. The pulverization method is not limited so long as
it does not impair the object of the present invention, and it may
be dry milling or may be wet milling. In the case of wet milling,
it is preferred to use water as the solvent. Here, for the
pulverization, a pulverizer such as a roll mill, a ball mill or a
jet mill may suitably be used. After the pulverization, the glass
may be dried or classified, as the case requires.
[0028] The glass powder as a component of the glass ceramic
composition preferably has a 50% particle diameter (D.sub.50) of
from 0.5 to 5 .mu.m. Here, in this specification, D.sub.50 is a
value calculated as the 50% value in the cumulative percent by
volume from the particle size distribution obtained by a laser
diffraction particle size distribution measurement.
[0029] The glass composition of the above glass powder is
preferably one which essentially comprises, as represented by
oxides, SiO.sub.2, B.sub.2O.sub.3, CaO and Al.sub.2O.sub.3. For
example, as the chemical composition of the glass powder, preferred
is one comprising, as represented by molar percentage as calculated
as oxides, from 57 to 65% of SiO.sub.2, from 13 to 18% of
B.sub.2O.sub.3, from 9 to 23% of CaO, from 3 to 8% of
Al.sub.2O.sub.3, from 0 to 6% of K.sub.2O, from 0 to 6% of
Na.sub.2O, and from 0.5 to 6% of K.sub.2O+Na.sub.2O.
[0030] With respect to the proportions of the glass powder and the
ceramic filler, preferred is one containing from 25 to 55 mass % of
the glass powder and from 45 to 75 mass % of the ceramic
filler.
[0031] In this case, the content of the ceramic filler is more
preferably at least 50 mass %, particularly preferably at least 55
mass %. If the content of the ceramic filler exceeds 75 mass %,
there is a possibility that it becomes difficult to obtain a dense
sintered body by firing, or smoothness of the substrate surface
tends to be impaired, and it is preferably at most 70 mass %.
[0032] The light emitting diode chip 3 is a GaN-type blue light
emitting diode chip that emits blue light, and a conductive
substrate made of e.g. a sapphire substrate or n-type SiC substrate
is used as a substrate for crystal growth. On the main surface side
of the substrate for crystal growth, a light emitting portion
formed by a GaN-type compound semiconductor material and having a
layered structure such as a double heterostructure, is grown by an
epitaxial growth method (for example, MOVPE method); on the back
surface of the substrate for crystal growth, a cathode electrode
(n-electrode) as a cathode side electrode (not shown), is formed;
and on the surface of the light emitting portion (the outermost
surface on the main surface side of the conductive substrate 11),
an anode electrode (p-electrode) as an anode-side electrode (not
shown) is formed. In short, on the light emitting diode chip, an
anode electrode is formed on one surface side, and a cathode
electrode is formed on the other surface side.
[0033] The wavelength conversion member 2 is disposed as overlaid
on the light emitting diode chip 3. The wavelength conversion
member 2 is constituted by a molded product of a mixture obtained
by mixing a transparent material such as a silicone resin and a
particulate yellow phosphor to be excited by blue light emitted
from the light emitting diode chip 3 to emit light of a broad
yellow type. Therefore, in the light emitting device 1 of this
embodiment, blue light emitted from the light emitting diode chip 3
and light emitted from the yellow phosphor, are radiated from the
light exit surface of the wavelength conversion member 2, whereby
white light can be obtained. Here, the transparent material to be
used for the wavelength conversion member 2 is not limited to a
silicone resin, and, for example, an acrylic resin, an epoxy resin
or glass may be employed. Further, the phosphor to be used for the
wavelength conversion member is not limited to the above-mentioned
yellow phosphor, and, for example, it is possible to obtain white
light also by mixing a red phosphor and a green phosphor.
Otherwise, so as to obtain light of a specific wavelength other
than white light, a suitable phosphor may be used.
[0034] As mentioned above, the wavelength conversion member 2 is
made of a phosphor and a resin or glass to disperse the phosphor,
and is strongly influenced by the heat generation of the light
emitting diode chip 3. Therefore, in addition to the effect of the
heating generation, the wavelength conversion member 2 is likely to
be deteriorated by reacting with the atmospheric air, whereby the
initial emission characteristics of the light emitting device may
not be maintained for a long period of time.
[0035] Therefore, by hermetically sealing the opening of the
package 5 by the cover glass 4, the contact between the wavelength
conversion member 2 and the atmosphere, is blocked to thereby
suppress the deterioration of the wavelength conversion member
2.
[0036] The cover glass 4 has an average thermal expansion
coefficient of from 45 to 70.times.10.sup.-7/.degree. C. in a
temperature range of from 0 to 300.degree. C. in order to maintain
the bonded state with the package 5 for a long period of time.
Thus, when a glass ceramic substrate is used as a substrate
material for the above described package 5, the difference in
thermal expansion coefficient from the cover glass 4 is small,
whereby it is possible to prevent that the bonded state of both is
destroyed by heat generation of the light emitting diode chip
3.
[0037] The average thermal expansion coefficient of the cover glass
4 in a temperature range of from 0 to 300.degree. C., is preferably
from 45 to 65.times.10.sup.-7/.degree. C., more preferably from 48
to 62.times.10.sup.-7/.degree. C.
[0038] Further, the package 5 and the cover glass 4 are preferably
bonded via a sealing material 6 containing a low melting point
glass which is melted by laser irradiation. By using such a bonding
method, it is possible to bond them reliably and firmly.
[0039] The sealing material 6 is provided on the package 5 side
surface of the cover glass 4, to seal the opening of the package 5.
Sealing material forming the sealing material 6, is one obtained by
adding an electromagnetic wave absorbing material (i.e. material
that generates heat by absorbing electromagnetic waves such as
laser light or infrared rays) to a sealing glass (i.e. glass frit)
made of low melting point glass. Further, a filler such as a
low-expansion filler may be added with a view to adjusting the
thermal expansion coefficient of the sealing material 6 or
improvement of the sealing strength, and further, other additives
may be contained as the case requires. Here, an additive such as an
electromagnetic wave absorbing material or a low-expansion filler,
is one so-called an inorganic filler.
[0040] As the sealing glass (glass frit), for example, low melting
point glass such as tin-phosphate glass, bismuth glass, vanadium
glass, lead glass, zinc borate alkali glass, etc. may be used.
Among these, it is preferred to use a sealing glass made of
tin-phosphate glass or bismuth glass, in consideration of adhesion
to the cover glass 4 and the package 5 and its reliability (e.g.
adhesion reliability and hermetic sealing property), and further in
consideration of e.g. the influence to the environment or the human
body.
[0041] The tin-phosphate glass (glass frit) preferably has a
composition comprising, by mol % calculated as the following
oxides, from 55 to 68 mol % of SnO, from 0.5 to 5 mol % of
SnO.sub.2 and from 20 to 40 mol % of P.sub.2O.sub.5 (basically the
total amount of these is made to be 100 mol %).
[0042] The bismuth glass (glass frit) preferably has a composition
comprising, by mass % calculated as the following oxides, from 70
to 90 mass % of Bi.sub.2O.sub.3, from 1 to 20 mass % of ZnO, from 2
to 12 mass % of B.sub.2O.sub.3 and from 0 to 20 mass % of
Al.sub.2O.sub.3 (basically the total amount of these is made to be
100 mass %).
[0043] The electromagnetic wave absorbing material may, for
example, be at least one metal (including its alloy) selected from
Fe, Cr, Mn, Co, Ni, Cu, In, Sn and Zn, as well as an oxide
containing at least one metal selected from the above metals, or a
transparent conductive oxide, such as ITO (Sn doped indium oxide),
or a tin oxide containing a dopant (ATO (Sb doped tin oxide) or FTO
(F doped tin oxide)). The particle diameter D.sub.50 of the
electromagnetic wave absorbing material is preferably from 0.1 to
30 .mu.m. It may be a pigment other than these.
[0044] Here, the amount of the electromagnetic wave absorbing
material is preferably made to be in the range of from 0.1 to 40
vol % to the sealing material. If the content of the
electromagnetic wave absorbing material is less than 0.1 vol %, it
may be impossible to sufficiently melt the sealing material. If the
content of the electromagnetic wave absorbing material exceeds 40
vol %, heat generation is likely to occur locally in the vicinity
of the interface with the package 5 or the cover glass 4, or
fluidity at the time of melting of the sealing material is likely
to be deteriorated, whereby adhesion to the package 5 or the cover
glass 4 tends to be lowered.
[0045] Further, as the low-expansion filler which may be added,
silica, alumina, zirconia, zirconium silicate, cordierite, a
zirconium phosphate compound, soda lime glass and borosilicate
glass may be mentioned. The low-expansion filler is one having a
thermal expansion coefficient lower than the sealing glass. The
content of the low-expansion filler is suitably adjusted so that
the thermal expansion coefficient of the sealing glass powder will
be close to that of the cover glass 4. The low-expansion filler is
preferably contained in a range of from 0.1 to 50 vol % in the
sealing material, although the content may depend also on the
thermal expansion coefficient of the sealing glass powder or the
cover glass 4.
[0046] Then, the sealing material as described above is mixed with
a vehicle to prepare a sealing material paste (i.e. a sealant). The
vehicle is one obtained by dissolving a resin as a binder component
in a solvent. The resin for the vehicle may, for example, be a
cellulose type resin, such as methyl cellulose, ethyl cellulose,
carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose,
propyl cellulose or nitrocellulose, or an organic resin such as an
acrylic resin obtainable by polymerizing at least one acrylic
monomer such as methyl methacrylate, ethyl methacrylate, butyl
methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate,
2-hydroxyethyl acrylate, etc. As the solvent, in the case of a
cellulose type resin, a solvent such as terpineol, butyl carbitol
acetate or ethyl carbitol acetate, and in the case of an acrylic
resin, a solvent such as methyl ethyl ketone, terpineol, butyl
carbitol acetate or ethyl carbitol acetate, is used.
[0047] The viscosity of the sealing material paste may be set to be
suitable for the apparatus for application to the cover glass 4,
and may be adjusted by the ratio of the resin (i.e. binder
component) to the solvent, or the ratio of the sealing glass
component to the vehicle. To the sealing material paste, known
additives to a glass paste, such as an antifoaming agent, a
dispersing agent, etc. may be added. In the preparation of the
sealing material paste, it is possible to employ a known method
using a rotary mixer equipped with a stirring blade, or a roll
mill, a ball mill or the like.
[0048] The average thermal expansion coefficient of this sealing
material in a temperature range of from 50 to 350.degree. C. is
preferably at most 90.times.10.sup.-7/.degree. C., more preferably
at most 88.times.10.sup.-7/.degree. C., further preferably at most
85.times.10.sup.-7/.degree. C. Further, it is preferably at least
30.times.10.sup.-7/.degree. C. If it is lower than this,
flowability of the sealing material tends to be so low that sealing
may not be conducted by using a laser beam.
[0049] It is thereby possible to reduce the amount of thermal
expansion of the sealing portion at the time of laser irradiation
and to prevent cracking caused by residual stress.
[0050] As the cover glass 4, it is possible to use one which
satisfies the above average thermal expansion coefficient and which
has a basic composition comprising, by mass % as calculated as the
following oxides, from 55 to 80% of SiO.sub.2, from 0.5 to 15% of
Al.sub.2O.sub.3, from 5 to 25% of B.sub.2O.sub.3, from 0 to 7% of
Li.sub.2O, from 0 to 15% of Na.sub.2O, from 0 to 10% of K.sub.2O
(provided Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%), less than
0.01% of ZrO.sub.2, from 0 to 0.1% of SnO.sub.2 and from 0.001 to
0.1% of Fe.sub.2O.sub.3, and has a glass composition containing
substantially no As.sub.2O.sub.3, Sb.sub.2O.sub.3 and PbO.
[0051] Further, as the cover glass 4, it is possible to use one
which satisfies the above average thermal expansion coefficient and
which has a basic composition comprising, by mass % as calculated
as the following oxides, from 55 to 80% of SiO.sub.2, from 0.5 to
15% of Al.sub.2O.sub.3, from 5 to 25% of B.sub.2O.sub.3, from 0 to
7% of Li.sub.2O, from 0 to 15% of Na.sub.2O, from 0 to 10% of
K.sub.2O (provided Li.sub.2O+Na.sub.2O+K.sub.2O=from 2 to 20%),
less than 0.01% of ZrO.sub.2, from 0 to 0.1% of SnO.sub.2 and from
0.003 to 0.1% of Fe.sub.2O.sub.3, and has a glass composition
containing substantially no As.sub.2O.sub.3, Sb.sub.2O.sub.3 and
PbO.
[0052] The reasons as to why the contents, etc. of the respective
components constituting the cover glass 4 in this embodiment are
defined as above will be described below. The contents of the
respective components are all represented by mass %.
[0053] SiO.sub.2 is a main component constituting the glass
skeleton and is a component for improving the durability of the
glass, but if it is less than 55%, the chemical durability cannot
be obtained, and if it exceeds 80%, the melting property will be
remarkably deteriorated. Preferably, it is from 58 to 75%.
[0054] Al.sub.2O.sub.3 is a component for improving the weather
resistance of glass, but if it is less than 0.5%, the chemical
durability tends to be insufficient, and if it exceeds 15%, striae
tend to be formed in the glass. Preferably, it is from 1 to
15%.
[0055] B.sub.2O.sub.3 is a component employed for the purpose of
improving the melting property and adjusting the viscosity, but if
it exceeds 25%, the weather resistance tends to decrease, and if it
is less than 5%, the melting property tends to be deteriorated.
Preferably, it is from 10 to 22%.
[0056] Li.sub.2O, Na.sub.2O and K.sub.2O will function as a flux
and are components for improving the devitrification resistance.
The contents of the respective components are preferably made to
be, by mass %, from 0 to 7% of Li.sub.2O, from 0 to 15% of
Na.sub.2O, and from 0 to 10% of K.sub.2O. If the respective
contents exceed the respective upper limits, the thermal expansion
coefficient is likely to become too large, or the weather
resistance is likely to be deteriorated. Here, the total content of
Li.sub.2O, Na.sub.2O and K.sub.2O (Li.sub.2O+Na.sub.2O+K.sub.2O)
shall be from 2 to 20%. If the total content of Li.sub.2O,
Na.sub.2O and K.sub.2O is less than 2%, the above effect will not
be obtainable, and if it exceeds 20%, the weather resistance tends
to be deteriorated, and the thermal expansion coefficient becomes
large.
[0057] Alkaline earth metal oxides (MgO, CaO, SrO, BaO) are
components effective for improving the melting property, weather
resistance and devitrification resistance, or adjusting the thermal
expansion coefficient, and may optionally be contained. For the
purpose of lowering the refractive index of the glass, SrO and BaO
are preferably not contained.
[0058] Fe.sub.2O.sub.3 is a component to prevent discoloration of
glass by ultraviolet solarization. The iron component is a
component that strongly absorbs ultraviolet radiation and thus is a
component which can be expected to provide a ultraviolet shielding
effect as is contained in a small amount in the glass, and it is an
essential component in an embodiment of the present invention, but
if Fe.sub.2O.sub.3 is less than 0.001% by mass %, its effect cannot
be expected, and if it exceeds 0.1%, the glass tends to be colored,
and the amount of transmitted light is likely to decrease.
Preferably, it is within a range of from 0.003% to 0.07%, more
preferably within a range of from 0.004% to 0.05%. The iron
component is present in different valence states of ions such as
Fe.sup.2+ and Fe.sup.3+ in the glass, and it causes coloration of
the glass as the ionic valence is converted by ultraviolet
irradiation. On the other hand, a portion colored by ultraviolet
irradiation serves as a film for shielding ultraviolet rays thereby
to prevent progression of the ultraviolet solarization by blocking
the ultraviolet radiation from entering into the glass. Therefore,
if the iron component content in the glass is small, holes formed
by the action of ultraviolet rays penetrated inside the glass
become light emission centers, and as a result, the transmittance
properties of the glass will be deteriorated. Based on such
coloration mechanism of glass due to ultraviolet rays,
Fe.sub.2O.sub.3 is required to be contained within a predetermined
range.
[0059] The iron component in glass is present in the form of
Fe.sub.2O.sub.3 and FeO, and in the present invention, it is meant
for a value obtained by calculating all of the iron component as
Fe.sub.2O.sub.3. Incidentally, Fe.sub.2O.sub.3 is a component for
improving the ultraviolet absorptivity, while FeO is a component
for improving the heat ray absorptivity. In order to let glass have
high transmittance, the proportion of FeO to the total iron oxide
is preferably less than 40%. The balance of Fe.sub.2O.sub.3 and FeO
can be controlled by adjusting the amounts of an oxidizing agent
and a reducing agent to be added to the glass raw material,
oxidation-reduction conditions in the glass melting furnace
atmosphere, etc.
[0060] Further, in addition to the method of adding the iron
component as a glass raw material, the iron component in glass may
be added by using either a method of addition by a silica sand
material by grasping the iron component contained in the silica
sand material, or a method of addition during the production
process by grasping the iron component to be mixed during the
production process, i.e. by a method of addition by a means other
than the raw material.
[0061] SnO.sub.2 is a component for preventing ultraviolet
solarization and may be contained, although it is not essential. In
a case where SnO.sub.2 is contained in an amount exceeding 0.1% as
calculated as SnO.sub.2, the ultraviolet absorbing performance of
glass tends to be high, and the transmittance of near ultraviolet
light tends to decrease, such being not desirable. The content of
SnO.sub.2 is preferably from 0.002 to 0.04%, more preferably from
0.002 to 0.015%. In the present invention, the Sn component is
defined by the content of SnO.sub.2, and this means that the
content of Sn (tin) contained in the glass composition, is within
the predetermined range as represented by a mass ratio, as
calculated as stannic oxide being an oxide. Other components in the
glass composition are likewise represented as calculated as their
specified oxides.
[0062] TiO.sub.2 is a component for preventing ultraviolet
solarization, and may be contained although it is not essential. If
TiO.sub.2 is contained in an amount exceeding 2% as calculated as
TiO.sub.2, the ultraviolet absorbing performance of glass tends to
be high and the transmittance of near ultraviolet light tends to
decrease, and at the same time, the refractive index tends to
increase, such being undesirable. The content of TiO.sub.2 is
preferably from 0.003 to 1.5%, more preferably from 0.005 to
1%.
[0063] Further, the cover glass 4 is required to be made so that
quality defects such as bubbles, foreign matters, etc. be as little
as possible and as small as possible (for example, at most 5
.mu.m). The cover glass of the present invention does not
substantially contain As.sub.2O.sub.3, Sb.sub.2O.sub.3 and PbO
which were used as clarifying agents in conventional glass, as they
are environmental load substances. Therefore, for the purpose of
clarification, it is preferred to suitably add a sulfate, a
nitrate, a chloride and/or a fluoride singly or in combination.
[0064] Each of such sulfate, nitrate, chloride and fluoride
components is a decomposable volatile component and will be
volatilized as an exhaust gas, and in considering of corrosion of
the exhaust gas treating device, and the cost for the treatment in
the glass production, the upper limit is preferably set to be at
most 0.5%. Further, in order to effectively diminish the foam, the
content is preferably set to be at least 0.005%. Such a content is
as calculated as an oxide in the case of a sulfate or a nitrate,
and as calculated as an element (CI, F) in the case of a chloride
or a fluoride.
[0065] The cover glass 4 is preferably adjusted so that the
transmittance at a wavelength of 365 nm in a thickness of 1 mm is
at least 85%. By doing so, it is possible to provide a light
emitting device suitable as a near ultraviolet light source.
[0066] The cover glass 4 is preferably adjusted so that the average
transmittance at a wavelength of from 808 to 1,064 nm in a
thickness of 1 mm is at least 85%. By doing so, when the package 5
and the cover glass 4 are to be bonded by using a sealing material
6, the laser beam to be used for melting the sealing material 6
will not be shielded by the cover glass 4, and it is possible to
quickly melt the sealing material 6.
[0067] The cover glass 4 is preferably adjusted so that the
refractive index (nd) is at most 1.52. By doing so, the reflection
loss at the surface is suppressed, and the transmittance becomes
high. The refractive index (nd) is more preferably at most 1.50,
more preferably at most 1.49. Here, the refractive index is the
refractive index of the d-line (590 nm).
[0068] Now, a method for producing the cover glass for
light-emitting diode package of the present invention will be
described.
[0069] Firstly, glass raw materials constituting the respective
components having desired compositions are prepared. Glass raw
materials to be utilized in the present invention, may be compounds
in any form, including oxides, hydroxides, carbonates, sulfates,
nitrates, fluorides, chlorides, etc.
[0070] Then, such raw materials are formulated into a glass raw
material so that glass having a desired composition will be
obtainable, and the raw material is put into a melting tank.
[0071] The melting tank is a container selected from platinum, a
platinum alloy and refractory. Here, the container selected from a
platinum alloy, is meant for a container made a platinum alloy
selected from the group consisting of alloys composed of platinum
(Pt), and one or a plurality of iridium (Ir), palladium (Pd),
rhodium (Rh) and gold (Au), and is one durable for high temperature
melting.
[0072] Glass melted in the melting tank is then subjected to
removal of bubbles and striae in a degassing vessel and a stirring
tank arranged on downstream side, whereby it is possible to obtain
a homogenized high quality glass which has little glass defect. The
obtained glass is molded into a predetermined shape by letting it
flow out via e.g. a nozzle, followed by cast molding in a mold, or
by pulling it out in the form of a rolled-out plate-shape. The
annealed glass is subjected to slicing, polishing or the like, to
obtain glass having a predetermined shape.
[0073] The cover glass for light emitting diode package of the
present invention is useful for a light emitting device comprising
a package having a light emitting diode mounted thereon (a glass
ceramic substrate in the above described example), a cover glass
for light emitting diode package, and a sealing material containing
a low melting point glass which is melted by laser irradiation to
bond the cover glass for light emitting diode package and the above
package (the glass ceramic substrate).
[0074] In such a construction, glass components are contained in
all of the cover glass for light emitting diode package, the glass
ceramic substrate as a light emitting diode package, and the
sealing material constituting the light emitting device, and
therefore, they can be bonded well without leading to a poor
reactivity as seen at the time of bonding between different types
of materials. Further, by adjusting the difference in the average
thermal expansion coefficient in a temperature range of from 25 to
300.degree. C. between the glass ceramic substrate and the cover
glass for light emitting diode package, to be at most
20.times.10.sup.-7/.degree. C., preferably at most
15.times.10.sup.-7/.degree. C., it is possible to provide
sufficient durability against a thermal shock during use of the
light-emitting device, and it is possible to maintain a high
hermetic sealing property over a long period of time.
[0075] Further, by making "the average thermal expansion
coefficient of the glass ceramic substrate".gtoreq."the average
thermal expansion coefficient of the cover glass for light emitting
diode package", it is possible to increase the substrate strength
against a thermal stress at the time of laser sealing of the cover
glass for light emitting diode package, and therefore, cracking of
the inorganic material substrate can be prevented, such being
preferred. The above relational expression means that in a
temperature range of from 25 to 300.degree. C., the average thermal
expansion coefficient of the glass ceramic substrate is at least
the average thermal expansion coefficient of the cover glass for
light emitting diode package.
[0076] Further, by satisfying the above relational expression, it
is possible to broaden the output width (output margin) of laser
light at the time of laser sealing of the cover glass for light
emitting diode package. The output of laser light is varied by e.g.
deterioration of the laser irradiation apparatus. The adhesion of
the sealing material depends on the output of laser light, and as
the output width of laser light whereby good adhesion can be
obtained becomes broad, stable production becomes possible with
less failure in adhesion.
[0077] Now, the present invention will be described with reference
to Examples.
[0078] The sample used in each Example (each of Ex. 1 to Ex. 15 and
Ex. 20 in Table 1 and Table 2) or each Comparative Example (each of
Ex. 16 and Ex. 17 in Table 2) was prepared in the following
manner.
[0079] Firstly, a glass raw material was formulated so as to have a
glass composition shown in Table 1 or Table 2, and using a platinum
crucible, this glass raw material formulation was subjected to
melting at a temperature of 1,550.degree. C. for 5 hours in an
electric furnace with a molybdenum silicide as a heating element,
followed by clarification and stirring. This glass was cast and
molded in a casting mold, followed by annealing to obtain 800 g of
a glass sample (glass block). Further, this glass block was
subjected to slicing and polishing to obtain a plate-form cover
glass for light emitting diode package, having a predetermined
shape (25 mm (vertical dimension).times.25 mm (horizontal
dimension).times.1 mm (thickness)).
[0080] With respect to the obtained glass, the average thermal
expansion coefficient in a temperature range of from 0 to
300.degree. C., the average thermal expansion coefficient in a
temperature range of from 25 to 300.degree. C., the transmittance
at a wavelength of 365 nm in a thickness of 1 mm (before
ultraviolet light irradiation and after irradiation with
ultraviolet light for 300 hours), the average transmittance at a
wavelength of from 808 to 1,064 nm in a thickness of 1 mm, and the
refractive index (nd), were measured. These results are shown in
Table 1 and Table 2. Here, in the evaluation results in Table 1 and
Table 2, the symbol "-" means "not measured".
TABLE-US-00001 TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7
Ex. 8 Ex. 9 SiO.sub.2 69.2 72.3 68.5 72.8 77.6 74.2 78.2 74.2 68.7
AL.sub.2O.sub.3 2.8 2.5 3.2 3.6 2.1 2.5 2.5 2.5 3.3 Fe.sub.2O.sub.3
0.005 0.007 0.017 0.007 0.007 0.010 0.024 0.032 0.043 Li.sub.2O 0.8
0.0 0.7 0.5 0.0 0.0 0.0 0.0 0.0 Na.sub.2O 0.4 7.4 0.4 6.0 6.7 7.4
7.4 7.4 7.4 K.sub.2O 8.1 1.0 8.3 1.5 0.0 1.0 1.0 1.0 1.0
B.sub.2O.sub.3 18.6 15.9 18.5 15.5 5.5 14.0 10.0 10.0 17.0 MgO 0.0
0.0 0.1 0.0 0.8 0.0 0.0 3.9 0.5 CaO 0.0 0.0 0.1 0.0 7.2 0.0 0.0 0.0
1.6 BaO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SrO 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 TiO.sub.2 0.0003 0.005 0.040 0.010 0.007 0.005
0.005 0.020 0.400 ZnO 0.0 0.8 0.0 0.0 0.0 0.8 0.8 0.8 0.0 Cl 0.0
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 SnO 0.02 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 SO.sub.3 0.004 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Sb.sub.2O.sub.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Total 100.0
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Average thermal
expansion coefficient 51 50 51 49 54 48 49 52 52 (0.degree. C. to
300.degree. C.) [.times.10.sup.-7/.degree. C.] Average thermal
expansion coefficient 44 -- -- -- -- -- -- -- -- (25.degree. C. to
300.degree. C.) [.times.10.sup.-7/.degree. C.] Transmittance 365 nm
(t1 mm) [%] 92.1 90.9 91.6 91.0 89.9 90.9 91.0 89.8 90.7 before
ultraviolet irradiation Transmittance 365 nm (t1 mm) [%] 73.1 89.5
89.9 89.2 84.8 90.2 86.6 86.2 89.4 after ultraviolet irradiation
Average transmittance 92.8 92.4 92.7 92.4 91.4 92.3 92.1 91.5 91.5
808 to 1,064 nm (t1 mm) [%] Refractive index (nd) 1.488 1.487 1.481
-- -- -- -- -- --
TABLE-US-00002 TABLE 2 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15
Ex. 16 Ex. 17 Ex. 20 SiO.sub.2 67.2 63.0 61.0 67.0 66.3 62.2 64.2
59.7 62.0 Al.sub.2O.sub.3 3.3 3.3 3.3 3.3 2.8 7.5 4.2 17.4 7.6
Fe.sub.2O.sub.3 0.007 0.007 0.007 0.007 0.010 0.008 0.0 0.0 0.002
Li.sub.2O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Na.sub.2O 7.4 7.4 7.4
7.4 10.0 10.0 6.4 0.0 9.95 K.sub.2O 1.0 1.0 1.0 1.0 0.0 0.1 6.5 0.0
0.0 B.sub.2O.sub.3 17.0 17.0 17.0 15.0 18.6 18.1 8.4 8.0 18.5 MgO
1.0 2.5 3.2 1.5 1.9 1.9 0.0 3.2 1.8 CaO 3.0 5.7 7.0 4.7 0.1 0.1 0.0
4.0 0.0 BaO 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 SrO 0.0 0.0 0.0 0.0
0.0 0.0 0.0 7.6 0.0 TiO.sub.2 0.010 0.015 0.005 0.008 0.100 0.008
4.3 0.0 0.0005 ZnO 0.0 0.0 0.0 0.0 0.0 0.0 5.9 0.0 0.0 Cl 0.1 0.1
0.1 0.1 0.1 0.1 0.0 0.0 0.06 SnO 0.0 0.0 0.0 0.0 0.02 0.02 0.0 0.0
0.02 SO.sub.3 0.0 0.0 0.0 0.0 0.02 0.01 0.0 0.1 0.02
Sb.sub.2O.sub.3 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 Total 100.0
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Average thermal
expansion coefficient 53 59 62 58 60 62 73 38 62 (0.degree. C. to
300.degree. C.) [.times.10.sup.-7/.degree. C.] Average thermal
expansion coefficient -- -- -- -- 61 63 72 38 -- (25.degree. C. to
300.degree. C.) [.times.10.sup.-7/.degree. C.] Transmittance 365 nm
(t1 mm) [%] 90.5 90.3 91.1 90.8 -- -- -- -- -- before ultraviolet
irradiation Transmittance 365 nm (t1 mm) [%] 89.4 89.7 89.8 90.0 --
-- -- -- -- after ultraviolet irradiation Average transmittance
91.0 90.8 91.9 91.3 91.1 92.2 -- -- -- 808 to 1,064 nm (t1 mm) [%]
Refractive index (nd) -- -- -- -- -- -- 1.520 -- --
[0081] The average thermal expansion coefficient in a temperature
range from 0 to 300.degree. C. was calculated by measuring the
elongation of glass with a dial gauge, by putting in thermostatic
baths at 0.degree. C. and 300.degree. C., samples processed into a
cylindrical shape with a diameter of 6 mm and a length of 100
mm.
[0082] Further, the average thermal expansion coefficient in a
temperature range of from 25 to 300.degree. C. was likewise
calculated by measuring the elongation of glass with a dial gauge,
by putting in thermostatic baths at 25.degree. C. and 300.degree.
C., samples processed into a cylindrical shape with a diameter of 6
mm and a length of 100 mm.
[0083] For the transmittance, with respect to glass having a
predetermined shape (25 mm (vertical dimension).times.25 mm
(horizontal dimension).times.1 mm (thickness)) which had both
surfaces optically polished to have a thickness of 1 mm, the
transmittance (wavelength of 365 nm, wavelength of from 808 to
1,064 nm) was measured by V-570 type ultraviolet visible near
infrared spectrophotometer (manufactured by JASCO Corporation).
Then, in accordance with the Japan Optical Glass Industry
Association Measuring Standard JOGIS-04, the glass was irradiated
with ultraviolet light for 300 hours, and thereafter, the
transmittance (wavelength 365 nm) of the glass was measured again,
whereupon the transmittance change before and after the ultraviolet
irradiation was compared.
[0084] As shown in Table 1 and Table 2, the respective glasses in
Examples have average thermal expansion coefficients within a range
of from 48 to 62.times.10.sup.-7/.degree. C., whereby when each
glass is bonded by a sealing material to a light emitting diode
package made of a glass ceramic substrate, because the degrees of
deformation in the plane direction of the respective members due to
thermal shock are similar, it is possible to maintain the hermetic
seal of inside of the package wherein a light emitting diode chip
is mounted, over a long period of time.
[0085] Further, with the respective glasses in Examples, the change
in transmittance at a wavelength of 365 nm before and after the
ultraviolet irradiation is small, whereby the initial emission
characteristics of the light emitting device can be maintained for
a long period of time.
[0086] Further, with the respective glasses in Examples, the
refractive index (nd) is at most 1.52, whereby the reflectance at
the front and back surfaces can be suppressed to be low in the
measurement of the transmittance, and it is possible to obtain a
high transmittance.
[0087] Whereas, with the respective glasses in Comparative
Examples, the average thermal expansion coefficient is outside the
range of the present invention, and it is concerned that such a
defect may occur that the output margin of laser light is narrow at
the time of sealing a sealing material containing low melting point
glass, by the laser, or such a problem may occur that cracking or
peeling results when the sealed structure is subjected to a
temperature cycle test.
[0088] Then, with respect to a light emitting device using the
cover glass of the present invention, the laser output and adhesion
were examined at the time of bonding the cover glass and a light
emitting diode package made of a glass ceramic substrate composed
of LTCC, as the package, by a sealing material containing low
melting point glass.
[0089] As the sealing material, the following material was
used.
[0090] As sealing glass, bismuth-type glass (softening point:
410.degree. C.) having a composition comprising, by mass % of the
following oxides, 83% of Bi.sub.2O.sub.3, 5% of B.sub.2O.sub.3, 11%
of ZnO and 1% of Al.sub.2O.sub.3 and having D.sub.50 of 1.0 .mu.m;
as a low-expansion filler, a cordierite powder having D.sub.50 of
4.3 .mu.m; and as an electromagnetic wave absorber, an ATO powder
having D.sub.50 of 1.0 .mu.m; were prepared.
[0091] D.sub.50 of the cordierite powder and ATO powder was
measured by using a particle size analyzer (Microtrac HRA,
manufactured by Nikkiso Co., Ltd.). Measurement conditions were
such that measurement mode: HRA-FRA mode, Particle Transparency:
yes, Spherical Particles: no, Particle Refractive index: 1.75, and
Fluid Refractive index: 1.33. Each powder was dispersed in water
and hexametaphosphate to obtain a slurry, which was then
ultrasonically dispersed, followed by the measurement.
[0092] Then, 60.7 vol % of the sealing glass, 26.1 vol % of the
cordierite powder and 13.2 vol % of the ATO powder were mixed to
prepare a sealing material (average thermal expansion coefficient
in a temperature range of from 50 to 350.degree. C.:
62.times.10.sup.-7/.degree. C.). Then, 83 mass % of the sealing
material and 17 mass % of a vehicle were mixed, and the mixture was
passed 7 times through a three-roll mill to sufficiently disperse
the cordierite powder and the ATO powder in the paste, to prepare a
sealing material paste. As the vehicle, a mixture comprising 5 mass
% of ethyl cellulose as an organic binder, and 95 mass % of
2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate as a solvent, was
used.
Ex. 18
[0093] The sealing material was applied by screen printing on a
cover glass (average thermal expansion coefficient in a temperature
range of from 0 to 300.degree. C.: 52.times.10.sup.-7/.degree. C.)
obtained by processing the glass of the above Ex. 1 to a size of 23
mm (vertical dimension).times.23 mm (lateral dimension).times.0.5
mm (thickness), followed by drying and firing to prepare a sealing
material layer-attached cover glass having a sealing material layer
formed on the surface.
[0094] Here, in the screen printing, a screen plate having a mesh
size of 200 and an emulsion thickness of 10 .mu.m, was used. Here,
the pattern of the screen plate was a circular pattern having a
line width of 0.5 mm and a radius of 20 mm. Further, the coating
layer of the sealing material was dried under conditions of
120.degree. C. for 10 minutes and then fired under conditions of
480.degree. C. for 10 minutes to form a sealing material layer
having a film thickness of 15 .mu.m and a line width of 0.5 mm on
the surface of the cover glass of Ex. 1.
[0095] Then, the above cover glass and a light emitting diode
package made of a glass ceramic substrate composed of LTCC (average
thermal expansion coefficient in a temperature range of from 25 to
300.degree. C.: 60.times.10.sup.7/.degree. C., size: 23 mm
(vertical dimension).times.23 mm (lateral dimension).times.1 mm
(thickness)) having no sealing material layer formed on the
surface, were laminated, and the sealing material layer was
irradiated with laser light through the above cover glass, to melt
the sealing material, followed by quenching and solidification to
seal the cover glass and the light emitting diode package.
[0096] As the laser light, a semiconductor laser was used, and the
laser light was applied with a spot diameter of 1.6 mm at a
scanning speed of 4 mm/sec, while changing the output within a
range of from 15 to 35 W. The intensity distribution of the laser
light was not shaped to be constant, and a laser beam having a
protrusion-like intensity distribution was used. As the spot
diameter at that time, the radius of the contour line where the
laser intensity became 1/e.sup.2 was used.
[0097] Further, for the output range of laser light useful for
sealing, the sealed portion was examined, and the output range and
the output width (output margin) were calculated where adhesion of
the sealed portion to the substrate was good, and neither cracking
of the cover glass nor peeling of the sealed portion was observed.
The results are shown in Table 3.
Ex. 19
[0098] The sealing material prepared by using the same sealing
material as in Ex. 18, was applied by screen printing on a
substrate (average thermal expansion coefficient in a temperature
range of from 0 to 300.degree. C.: 38.times.10.sup.-7/.degree. C.)
obtained by processing the glass in Ex. 17 to a size of 23 mm
(vertical dimension).times.23 mm (lateral dimension).times.0.5 mm
(thickness). Then, in the same manner as in Ex. 18, the sealing
material was melted by irradiation with laser light, followed by
quenching and solidification to seal the cover glass and the light
emitting diode package. Then, the output range of laser light
wherein the glass in Ex. 17 and the light emitting diode package
made of LTCC can be sealed, was examined, and the margin of the
laser output was calculated. The results are shown in Table 3.
[0099] The sealed structure in each of Ex. 18 and Ex. 19
(hereinafter one having a cover glass for light-emitting diode
package and a light emitting diode package (typically a glass
ceramic substrate) bonded to each other, will be referred to as a
sealed structure having a cover glass and a light emitting diode
package bonded), was subjected to a temperature cycle test (1
cycle: from -40 to 150.degree. C., 200 cycles). Before and after
the temperature cycle test, the presence or absence of cracking and
peeling occurred at the sealed portion between the glass and the
light-emitting diode package made of LTCC, was observed. These
results are summarized in Table 3. Ex. 18 is an Example of the
present invention, and Ex. 19 is a Comparative Example.
TABLE-US-00003 TABLE 3 Ex. 18 Ex. 19 Cover glass Glass Glass in Ex.
1 in Ex. 17 Evaluation Output range [W] of laser light 20 to 24 22
of sealing capable of sealing property output margin [W] of laser
light 5 1 Presence or absence of cracking Absent Present and
peeling after temperature cycle test
[0100] As shown in Table 3, in Ex. 18, no cracking or peeling was
observed after the temperature cycle test, and it is evident that
it is thereby possible to maintain good sealed conditions. Whereas,
in Ex. 19, the average thermal expansion coefficient of the glass
used (glass in Ex. 17) was outside the range of the present
invention, and cracking and peeling were observed after the
temperature cycle test.
[0101] Further, in Ex. 18 wherein the difference in the average
thermal expansion coefficient is small between the glass and the
light emitting diode package made of the glass ceramic substrate
composed of LTCC, the output margin of laser light is broad,
whereby stable production is possible as adhesion failure is less
likely to occur. In contrast, in Ex. 19 wherein the difference in
the average thermal expansion coefficient was large between the
glass and the light-emitting diode package made of the glass
ceramic substrate composed of LTCC, the output margin of laser
light was narrow, whereby adhesion failure was likely to occur due
to output variations of the laser light.
INDUSTRIAL APPLICABILITY
[0102] According to the present invention, it is possible to
provide a cover glass for light emitting diode package, a sealed
structure and a light emitting device, capable of preventing
deterioration of the transmittance characteristics during the use
for a long period of time.
[0103] This application is a continuation of PCT Application No.
PCT/JP2014/082305, filed on Dec. 5, 2014, which is based upon and
claims the benefit of priority from Japanese Patent Application No.
2013-256170 filed on Dec. 11, 2013. The contents of those
applications are incorporated herein by reference in their
entireties.
REFERENCE SYMBOLS
[0104] 1: light emitting device, 2: wavelength conversion member,
3: light emitting diode (light emitting diode chip), 4: cover glass
for light emitting diode package, 5: light emitting diode package
(glass ceramic substrate), 6: sealing material.
* * * * *